Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 191725

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1225 PM CDT Mon Jun 19 2017

.SHORT TERM...  (Through Late Tonight)
Issued at 355 AM CDT Mon Jun 19 2017

Mid level clouds will advect southeastward into our forecast area
this morning ahead of a weak northwest flow shortwave.  The HRRR
model runs were depicting at least isolated convection this
afternoon.  It appears that any forcing will be weak and low level
moisture will be limited so the high resolution models may be
overdone in generating convection, but still feel that isolated
light showers will be possible this afternoon.  Will include slight
chance pops this afternoon across northeast into central MO and west
central IL.  High temperatures today will be a couple of degrees
warmer than the previous day, and close to seasonal normals. Another
batch of mid level clouds will drop southeastward into our area late
tonight with low temperatures a couple of degrees warmer than
this morning and slightly below normal.


.LONG TERM...  (Tuesday through Sunday)
Issued at 355 AM CDT Mon Jun 19 2017

NW flow aloft will prevail for the period from Tuesday to Wednesday.
 This is expected to facilitate a surface cold front dropping into
our northern CWA late Tuesday afternoon where it will stall into
Tuesday night before heading back north as a warm front on
Wednesday.  Moisture thru the column and low level convergence
should be sufficient by late Tuesday afternoon to support the
potential for isolated thunderstorms and this threat could continue
across areas north of I-70 until Wednesday when the front pushes
north.  Have introduced slight chance PoPs from Tuesday afternoon
thru Wednesday morning--for now, for areas in northern MO and
central IL--to account for this.  Temps for areas south of the
anticipated position of the front during this period will continue
to build, with daytime max temps edging higher each day, into the
lower 90s in places by Wednesday, but humidities should be low
enough to preclude any dangerous heat issues.

The flow aloft becomes zonal for much of the central CONUS for
Thursday thru Saturday with a series of upper level disturbances
expected to train thru our region.  The better moisture and
instability is anticipated to initially be across northern MO and
central IL on Thursday, where the rain chances will be, with this
expanding areawide concurrently with a cold front dropping thru on
Friday.  As it stands now, Friday looks to be the best chance for
widespread rain for the week.  The cold front push thru our region
for late week should also bring to an end another very warm stretch
of temps.

Models diverge significantly for Saturday, with the GFS advertising
a single frontal push with high pressure and dry wx building in for
the upcoming weekend.  The EC, in contrast, promptly buckles the
front northward only to pass it thru again on Saturday night,
effectively extending rain chances by at least another 24hrs.  With
such low confidence on features for next weekend, climo looks like
the best route to take for now, edging temps downward and
maintaining mentionable low PoPs.

The model consensus appears to resume by the end of next weekend
with a cool high pressure building in and what should be dry wx.



.AVIATION...  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1219 PM CDT Mon Jun 19 2017

NW flow aloft and at the sfc will continue this afternoon. Expect
isod to widely sct SHRA this afternoon which may impact all
terminals. Can not completely rule out an isod TS, but this
currently seems less likely.

Clouds are expected to dissipate shortly after sunset this
evening. Winds will also diminish and back to become more wly to
wswly. Winds are expected to pick up slightly on Tues morning and
become wly to nwly again.





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